**Colleen B. Bove1,2*, Laura Mudge1,3, and John F. Bruno1**


1 The Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, 27599-3280 USA

2 The Department of Biology, Boston University, Boston, Massachusetts, 02215 USA

3 Integral Consulting Inc., Annapolis, Maryland 21401 USA

*Corresponding author: colleenbove@gmail.com


Abstract:

Anthropogenic climate change is rapidly altering the characteristics and dynamics of biological communities. This is especially apparent in marine systems as the world’s oceans are warming at an unprecedented rate, causing dramatic changes to coastal marine systems, especially on coral reefs of the Caribbean. We used three complementary ocean temperature databases (HadISST, Pathfinder, and OISST) to quantify change in thermal characteristics of Caribbean coral reefs over the last 150 years (1871–2020). These sea surface temperature (SST) databases included combined in situ and satellite-derived SST (HadISST, OISST), as well as satellite-only observations (Pathfinder) at multiple spatial resolutions. We also compiled a Caribbean coral reef database identifying 5,326 unique reefs across the region. We found that the Caribbean reefs have warmed on average by 0.20 °C per decade since 1987, the calculated year that rapid warming began on Caribbean reefs. Further, geographic variation in warming rates ranged from only 0.17 °C per decade on Bahamian reefs to 0.26 °C per decade on reefs within the Southern and Eastern Caribbean ecoregions. If this linear rate of warming continues, these already threatened ecosystems would warm by an additional 1.6°C on average by 2100 across the Caribbean. We also found that marine heatwave (MHW) events are increasing in both frequency and duration across the Caribbean. Caribbean coral reefs now experience on average 5 MHW events annually, compared to 1 per year in the early 1980s. Combined, these changes have caused a dramatic shift in the composition and functioning of Caribbean coral reef ecosystems. If reefs continue to warm at this rate, we are likely to lose even the remnant Caribbean coral reef communities of today in the coming decades.


Citation:

Citation will go here


Caribbean Ecoregion Coral Reefs

Figure 1

FALSE OGR data source with driver: ESRI Shapefile 
FALSE Source: "/Users/colleen/Dropbox/Git/CaribbeanSST/data/EcoRegions", layer: "Caribbean_ecoregions"
FALSE with 17 features
FALSE It has 9 fields

Caribbean coral reef site locations and ecoregion designation. The colour of each reef represents the designated ecoregion (Spalding et al. 2010) and n denotes the number of unique reefs within that ecoregion.


SST Extraction and Analysis

Figure 2

Historic SST trend on Caribbean coral reefs (1871–2020). Long-term SST records (HadISST) on Caribbean coral reefs depicting A) mean monthly SST each year (represented by line colour: blue to red) and B) GAM smoothed annual mean SST time (black line), annual maximum (red line), and annual minimum (blue line) SST. The grey dashed horizontal line denotes the overall mean SST for all sites over the entire period (27.3 °C) and the grey ribbon represents the 95% confidence interval around the true annual SST mean through time.


Figure 3

Historic SST trends on coral reefs within ecoregions (1871–2019). Long-term SST records (HadISST) on Caribbean coral reefs separated by ecoregion depicting GAM smoothed annual mean SST time (black line), annual maximum (red line), and annual minimum (blue line) SST. The grey dashed horizontal line denotes the mean SST over the entire period and the grey ribbon represents the 95% confidence interval around the true annual SST mean for each ecoregion.


Figure S2

Historic SST trend on Caribbean coral reefs (1871–2020). Long-term SST records (HadISST) on Caribbean coral reefs depicting significant changes in warming rate based on the first derivative of the GAM modelled slope. The GAM smoothed annual mean SST time is represented by the black line with significantly positive (red) or negative (blue) identified over the curve. The most recent significant warming event began in 1987 and is highlighted in the yellow box. The annual maximum (red line) and annual minimum (blue line) SST are also depicted, along with the overall mean SST for all sites over the entire period (27.3 °C; grey dashed line). The grey ribbon represents the 95% confidence interval around the true annual SST mean through time.


Figure S3

Historic SST records (1981-2019; Pathfinder) on Caribbean coral reefs depicting A) mean monthly SST each year (represented by line colour: blue to red) and B) GAM smoothed annual mean SST time (black line), annual maximum (red line), and annual minimum (blue line) SST. The grey dashed horizontal line denotes the overall mean SST for all sites over the entire period (27.23 °C) and the grey ribbon represents the 95% confidence interval around the true annual SST mean through time.


Figure S4

Comparison of HadISST (1871–2020) and Pathfinder (1981-2019) SST recorded on Caribbean coral reef locations. The high-resolution Pathfinder is represented as darker data over the long-term HadISST. Both datasets are represented by GAM smoothed annual mean SST time (solid line), annual maximum (red line), and annual minimum (blue line) SST. The dashed horizontal line denotes the overall mean SST for all sites over the entire period and the grey ribbon represents the 95% confidence interval around the true annual SST mean through time.


Figure S5

Historic SST trends on coral reefs within Caribbean ecoregions (1871–2020) with corresponding reef locations (see Figures 1, 3 in the main text). The colour of each reef location and box around long-term SST (HadISST) plots represent the designated ecoregion. Plots depict SST data with GAM smoothed annual mean SST time (black line), annual maximum (red line), and annual minimum (blue line) SST. The grey dashed horizontal line denotes the mean SST over the entire period and the grey ribbon represents the 95% confidence interval around the true annual SST mean for the A) Bahamian, B) Eastern Caribbean, C) Floridian, D) Greater Antilles, E) Gulf of Mexico, F) Southern Caribbean, G) Southwestern Caribbean, and H) Western Caribbean ecoregions.


HadISST GIF

Long-term SST records (HadISST) on Caribbean coral reefs depicting mean monthly SST each year (represented by line colour: blue to red).


Caribbean Basin Maps and Marine Heatwaves

Figure 4

All Marine Heatwave analyses were performed by Laura Mudge (GitHub: Lmudge13)

Laura's code/analyses are included in this script and identified within code chunks when pulled or modified from her original work.

Warming patterns throughout the Caribbean Sea. Increasing warming events across the Caribbean depicted through A) rate of SST change (°C per decade) from 1981 to 2019 (Pathfinder; mean slope 0.23 ± 0.087 °C per decade) and B) increasing marine heatwave events (slope of counts per year). Grey ocean area was not included in these analyses.


Figure 5

MHW trends (1981–2018) across Caribbean coral reefs. Temperature data are based on OISST gridded data to determine A) marine heat wave (MHW) frequency (number events per year) with Nagelkerke pseudo R2; B) MHW duration (number days per event) with linear model R2 ; and C) return time (number days per event) since the previous MHW event with linear model R2 reported. Points denote annual mean values (±SD) and blue lines represent linear (lm or glm) trends.


Figure S6

Significance of A) rate of SST change (°C per decade) and B) number of marine heatwave events per year across the Caribbean depicted in Figure 4. Grey ocean area was not included in these analyses.


Figure S7

A) Rate of SST change (°C per decade) over the duration of the HadISST database across the Caribbean from 1871 to 2020 (mean slope 0.04 ± 0.014 °C per decade) and B) significance of rate of SST change. Grey ocean area was not included in these analyses.


Figure S8

A) Rate of SST change (°C per decade) across the Caribbean from 1981 to 2020 (HadISST; mean slope 0.17 ± 0.046 °C per decade) and B) significance of rate of SST change. Grey ocean area was not included in these analyses.


Figure S9

MHW trends (1981–2018) across Caribbean coral reefs by ecoregion. Temperature data are based on OISST gridded data to determine frequency (number events per year), duration (number days per event), return time (number days per event) since the previous event, onset rate (°C per day) from start until peak intensity, peak intensity (°C), and total days reefs experience MHWs per year. Points denote annual mean values (±SD) and blue lines represent linear (lm or glm) trends within each ecoregion (see Figures 1, S5 for ecoregion locations). Frequency, duration, and return time across all Caribbean coral reefs are depicted in Figure 5 in the main text.


Tables

Table 1

Table 1. Estimated warming rates from both HadISST and Pathfinder databases for different temporal ranges. Values are means of all 5,326 reef locations included in the study. The year 1987 was estimated as the beginning of the most recent period of warming across all Caribbean coral reefs (see Figure S2).

Temperature parameter HadISST (1871-2020) HadISST (1981-2020) HadISST (1987-2020) Pathfinder (1981-2019) Pathfinder (1987-2019)
Caribbean Basin (°C per decade) 0.04 0.17 0.18 0.23 NA
Caribbean Basin (total °C for period) 0.60 0.68 0.61 0.90 NA
Caribbean Reefs (°C per decade) 0.04 0.15 0.16 0.19 0.2
Caribbean Reefs (total °C for period) 0.60 0.60 0.54 0.74 0.66

Table 2

Table 2. Published reports of global ocean surface warming rates.

Study °C per decade Years
Casey and Cornillon 2001 55 0.14 1960–1990
Lawrence et al. 2004 56 0.09 - 0.13 1985–2000
Good et al. 2007 57 0.17 1985–2004
Burrows et al. 2011 58 0.07 1960–2009
USGCRP 2017 59 0.15 1900–2016

Table S1

Table S1. Marine heatwave properties examined in this study

Metric Units Description
Frequency Number of events Number of discrete mhw events
Total MHW days days The total number of days a location experienced a MHW per year
Duration days The number of days between the start and end date of each distinct MHW event
Peak intensity °C The maximum temperature, above the seasonal varying climatological mean, reached during the MHW event
Onset rate °C per day “Rate of temperature change between onset date and date of peak intensity”
Return time days The number of days elapsed since a previous mhw event in that location

Table S2

Table S2. Mean ocean warming rate (°C per decade; with 95% confidence interval) and total increase in temperature (°C) on coral reefs within each Caribbean ecoregion since the noted year of inflection point. The inflection point for each ecoregion was identified as the year in which annual warming rates noticeably increased based on the GAM smoothed annual means (see Figures 3 and S5). Years indicated with an asterisk (*) represent inflection points identified for ecoregions that occurred before the Pathfinder dataset record, therefore those rates and total warming values were calculated from the beginning of the record in 1981.

Ecoregion Inflection point Mean rate (°C per decade) Lower confidence interval Upper confidence interval Warming extent (°C)
Bahamian 1988 0.17 0.161 0.182 0.53
Eastern Caribbean 1984 0.26 0.260 0.267 0.91
Floridian 1993 0.22 0.207 0.231 0.57
Greater Antilles 1986 0.16 0.160 0.168 0.53
Gulf of Mexico 1981 0.21 0.186 0.241 0.80
Southern Caribbean 1981 0.26 0.258 0.268 0.99
Southwestern Caribbean 1982 0.20 0.194 0.204 0.74
Western Caribbean 1999 0.24 0.235 0.253 0.48

Table S3

Table S3. Model results for MHW trends on coral reefs in the Caribbean basin between 1981-2018. Frequency was modeled using a glm model with poisson distribution and log link. Estimates, standard error, z scores (statistic), and p-values are reported. Nagelkerke pseudo r-squared used to assess goodness of fit. MHW duration and return time were log transformed before modeling with ols models. Estimate, standard error, t value (statistic) and p-value are reported along with multiple and adjusted r-squared.

Estimate Standard error Statistic P-value
Frequency
(Intercept) -93.154 0.892 -104.406 < 0.001
year 0.047 0.000 105.559 < 0.001
R2 0.480
Duration
(Intercept) -36.508 0.666 -54.790 < 0.001
year 0.019 0.000 58.157 < 0.001
R2 0.185
Return Time
(Intercept) 87.968 1.668 52.750 < 0.001
year -0.041 0.001 -49.840 < 0.001
R2 0.148

Table S4

Table S4. Mean decadal value of MHW parameters (frequency, duration, and return time) for the entire basin and by ecoregion.

Region 1980 1990 2000 2010
Duration (days)
Caribbean 7.6 8.3 10.8 14.5
Bahamian 8.6 8.6 10.3 12.8
Eastern Caribbean 6.9 8.1 15.0 19.0
Floridian 8.9 9.5 9.6 11.3
Greater Antilles 7.3 7.9 11.1 14.4
Gulf of Mexico 8.2 10.8 9.5 14.6
Southern Caribbean 7.5 7.5 10.3 15.7
Southwestern Caribbean 7.3 7.5 9.6 15.3
Western Caribbean 7.1 8.4 8.9 11.4
Frequency (events per year)
Caribbean 1.2 1.6 2.8 4.3
Bahamian 1.6 2.0 2.6 4.2
Eastern Caribbean 0.5 1.0 2.7 4.1
Floridian 1.2 2.7 2.5 5.4
Greater Antilles 1.2 1.5 2.9 4.4
Gulf of Mexico 1.5 2.0 3.0 4.1
Southern Caribbean 1.0 1.2 2.9 4.5
Southwestern Caribbean 1.2 1.4 3.1 4.7
Western Caribbean 1.6 2.0 2.7 3.2
Return Time (days)
Caribbean 376.7 373.2 202.4 110.8
Bahamian 304.6 264.9 201.3 122.2
Eastern Caribbean 721.9 651.1 236.3 94.9
Floridian 334.2 234.7 182.0 83.1
Greater Antilles 398.9 435.0 202.1 107.8
Gulf of Mexico 364.9 247.7 158.2 133.6
Southern Caribbean 327.8 442.4 202.6 106.4
Southwestern Caribbean 449.2 422.2 194.1 96.2
Western Caribbean 299.3 257.8 204.7 145.9

Session information

All code was written by Colleen B. Bove, feel free to contact with questions.

Session information from the last run date on 2021-04-20:

## R version 3.6.3 (2020-02-29)
## Platform: x86_64-apple-darwin15.6.0 (64-bit)
## Running under: macOS High Sierra 10.13.6
## 
## Matrix products: default
## BLAS:   /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRblas.0.dylib
## LAPACK: /Library/Frameworks/R.framework/Versions/3.6/Resources/lib/libRlapack.dylib
## 
## locale:
## [1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
## 
## attached base packages:
## [1] splines   grid      stats     graphics  grDevices utils     datasets 
## [8] methods   base     
## 
## other attached packages:
##  [1] transformr_0.1.3    fmsb_0.7.0          performance_0.7.1  
##  [4] modelr_0.1.8        broom_0.7.6         sjPlot_2.8.7       
##  [7] ggpubr_0.4.0        gridExtra_2.3       repmis_0.5         
## [10] kableExtra_1.3.4    plotly_4.9.3        foreach_1.5.1      
## [13] mgcv_1.8-34         nlme_3.1-152        Hmisc_4.5-0        
## [16] Formula_1.2-4       survival_3.2-10     lattice_0.20-41    
## [19] gganimate_1.0.7     fields_11.6         spam_2.6-0         
## [22] dotCall64_1.0-1     binr_1.1            gapminder_0.3.0    
## [25] gifski_1.4.3        RColorBrewer_1.1-2  xts_0.12.1         
## [28] zoo_1.8-9           rnaturalearth_0.1.0 forcats_0.5.1      
## [31] stringr_1.4.0       dplyr_1.0.5         purrr_0.3.4        
## [34] readr_1.4.0         tidyr_1.1.3         tibble_3.1.0       
## [37] tidyverse_1.3.0     openxlsx_4.2.3      rgdal_1.5-23       
## [40] maptools_1.1-1      viridis_0.5.1       viridisLite_0.3.0  
## [43] raster_3.4-5        sp_1.4-5            ggrepel_0.9.1      
## [46] ggplot2_3.3.3       ncdf4_1.17          sf_0.9-8           
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##   [1] utf8_1.2.1              R.utils_2.10.1          tidyselect_1.1.0       
##   [4] lme4_1.1-26             htmlwidgets_1.5.3       lpSolve_5.6.15         
##   [7] munsell_0.5.0           codetools_0.2-18        effectsize_0.4.4-1     
##  [10] units_0.7-1             statmod_1.4.35          withr_2.4.1            
##  [13] colorspace_2.0-0        highr_0.8               knitr_1.31             
##  [16] rstudioapi_0.13         ggsignif_0.6.1          labeling_0.4.2         
##  [19] emmeans_1.5.5-1         rnaturalearthdata_0.1.0 farver_2.1.0           
##  [22] coda_0.19-4             vctrs_0.3.7             generics_0.1.0         
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